The present invention relates to a ceramic clay, a ceramic formed article, a ceramic structure, and methods of manufacturing them. In more detail, the present invention relates to a ceramic clay, a ceramic formed article, a ceramic structure, and methods of manufacturing them, capable of preventing or reducing generation of CO2 or harmful gas during firing to thereby prevent or inhibit pollution, and global warming, when used in manufacturing a ceramic structure, and capable of obtaining a high-strength honeycomb structure having few defects such as cracks.
To form a ceramic product, in general, methods such as spinning lathe forming, extrusion forming, injection forming, press forming, and sheet forming have been used. However, since plasticity/shape retaining property and the like required for the forming cannot be obtained only by a ceramic material powder. Therefore, after adding water, organic binder and the like to thereby form a ceramic forming material, the material is formed. For example, a method of manufacturing a ceramic structure has been disclosed in which in the extrusion forming, a ceramic material, water, organic binder and the like are kneaded, and the forming material (clay) whose plasticity has been enhanced is extruded, dried, and fired (see, e.g., Japanese Patent No. 3227039).
When an added amount of the organic binder imparting the plasticity or the shape retaining property increases, the forming property of ceramic is enhanced. For example, in the extrusion forming, to form a large-sized structure or a structure having a complicated cell structure which has been increasingly demanded in recent years, kneaded clay having a satisfactory forming property is required as compared with a case where a small-sized or simple ceramic structure is manufactured. As a result, a large amount of organic binder has to be added.
However, when the added amount of the organic binder is large, the organic binder burns down during firing. Therefore, there has been a problem that a space occupied by the organic binder becomes a defect at a forming time, and mechanical strength of the structure drops. In a large-sized structure, there has been a problem that the inside of the structure is at high temperature by burning heat when burning the organic binder during the firing, defects such as cracks are generated because of thermal stress by an inner/outer temperature difference of the structure, the mechanical strength of the structure is lowered, and yield is largely lowered. Furthermore, CO2 or harmful gas is generated, and released to the atmosphere by the burning of the organic binder during the firing, and this has raised a problem in environmental respects such as pollution and global warming.
On the other hand, clay (Gairome clay, etc.) which is a pottery material has such plasticity that forming is possible, even when the above-described organic binder is not contained. As a factor for this material to develop the plasticity, particles are fine, shape is flat or needlelike, and hydrogen bond is caused with respect to water (See pp. 828 to 830 of Clay Handbook Version 2 (GIHODO SHUPPAN Co. 1987)). Attempts have been made to add a compound having such characteristic to a ceramic material powder as in a conventional organic binder, and accordingly impart plasticity to the ceramic material clay (see pages 175 to 178 of Artificial Clay (10th Anniversary Journal of Artificial Clay Research Institute), and The Use of Montmorillonites as Extrusion Aids for Alumina, Ceram. Engi. Sci. Proc. 12 [1-2] pp. 33 to 48 (1991)).
However, with regard to clay minerals disclosed in the above-described documents and having plasticity, such as bentonite and smectite, naturally produced minerals contain a large amount of impurities, and it is feared that the products run out in near future, and there has been a problem that synthetic compounds or refined natural products are expensive as compared with the organic binders.
The present invention has been developed in view of the above-described problems, and an object thereof is to provide a ceramic clay, a ceramic formed article, a high-strength ceramic structure, and methods of efficiently manufacturing them, capable of preventing or reducing generation of CO2 or harmful gas during firing to thereby prevent or inhibit pollution and global warming, when used in manufacturing a ceramic structure, and capable of obtaining a high-strength ceramic structure having few defects such as cracks.